The invention relates to a down-flow chamber, in which, from a filter in the ceiling of a working room, an air flow free of germs and dust is directed downwardly on a working face surrounded by walls with exhaust openings for the air flow at the front and the back.
At the front of the chamber a transparent wall is provided and between the lower edge of that wall and an exhaust grid in front of the working face there is a vertical slit or opening of such a height that the arms, protected by gloves with long gauntlets, can be put through the slit to carry out activities in the working room.
Through the slit materials and additional means can also be brought into the working room.
The large exhaust grid in front of the working face has a great capacity so that air is sucked in both from within the chamber and from its outside.
Hence an air curtain is provided that prevents ambient air from entering the working room and further, prevents the air in the working room from escaping directly into the ambient atmosphere.
The air supplied from above through the filter sweeps past the inner surface of the transparent front wall and the ambient air sweeps past the outer surface of the same.
If the exhaust capacity of the grid is not great enough or is hampered, contaminated air can flow from the inside to the outside or from the outside to the inside.
When in the working room viruses or bacteria or other dangerous products are handled that should under no condition escape from the chamber according to the invention, at the lower edge of the transparent wall a flexible lid, preferably of smooth plastics material is provided, that is hanging down and substantially extends to the exhaust grid and highly reduces the area of the vertical slit.
In order to be able to operate in the chamber, the arms are passed under the lid that is hanging down and it is lifted inwardly, the outer surface of the lid being in contact with the gauntlets over the arms.
The air flow in the working room along the transparent wall then is guided downwardly past the inner surface of the lid and disappears in the exhaust grid.
The air leakage flow past the outer surface increases by lifting the lid because it is sucked by a larger part of the exhaust grid.
Because the lower edge of the lid lies lower than the lower edge of the transparent wall and the air leakage flow has increased, the risk of vortexes, that might emerge under the lower edge of the lid to ambient air, is much smaller and, thus theoretically not one particle would be able to escape out of the working room to ambient air.
It has been found, however, that in withdrawing the arms the flexible lid is drawn along outwardly, while its inner surface sweeps over the gauntlets and thus transfers on to the gauntlets particles adhering to this surface. In this manner the particles are introduced directly into the ambient air with the gauntlets.
Moreover the air flow past the inner surface of the lid is guided to ambient air, while the air leakage flow is strongly reduced when the lower edge of the lid is able to move away from the zone of the exhaust grid.
Upon this occurrence, the vortexes of the inner air flow can escape from the working room under the lower edge of the lid to ambient air, thus taking along particles to ambient air.